The present invention relates to data storage systems, and more particularly, this invention relates to storage conditions for magnetic tape in data storage systems.
In magnetic storage systems, magnetic transducers read data from and write data onto magnetic recording media. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media. Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.
In a typical tape drive, multiple tracks are written to and/or read from a magnetic tape simultaneously. Moreover, data tracks on magnetic tapes are continually made smaller (in the cross-track direction) in an attempt to increase track density. However, as data tracks continue to become smaller, it becomes more difficult to ensure that data is written in the intended location on magnetic tape. This is particularly true for situations involving track misregistration which indicates a mismatch exists between the intended data track writing and/or reading location, and the actual data track writing and/or reading location.
Track misregistration can occur when the physical dimensions of a magnetic tape change between a time that data is written to the tape and a time that the data is read back from the tape. This dimensional instability may be caused by changes in temperature, humidity, or long term creep of the media caused by stresses exerted on the magnetic tape. For instance, when a magnetic tape is not in use, it is typically wrapped onto a tape spool for storage. Due to the length of magnetic tapes, numerous wraps of the magnetic tape are layered on top of each other, extending radially outward from the center of the tape spool. This process of winding the magnetic tape onto the spool causes a compressive stress to be imposed on the magnetic tape in the radial direction. In other words, each wrap of the magnetic tape exerts a compressive stress on the layers positioned therebelow.
Tape media is a viscoelastic material having both energy storage and energy dissipative mechanisms. Thus, the compressive stress experienced by a magnetic tape while wound on a spool may cause at least a portion of the tape to widen (deform) in the cross-track direction. However, after this compressive stress is applied to a magnetic tape, at least some of the dimensional deformation experienced by the tape will not be recoverable. This phenomenon is known as “creep”. Tape creep may also be dependent on the temperature and humidity the magnetic tape is stored in, as hot and humid conditions tend to accelerate the creep process. Over time, creep may be sufficient enough to cause data tracks to be misaligned compared to the position that they were written in, thereby making it difficult or even impossible to read the data stored thereon in a single pass.